Fillers

ABSTRACT

A cohesive polymer matrix comprising a matrix polymer and a coated particulate filler dispersed therein, characterized in that the matrix polymer is a solution rubber, and the filler is coated at least in part with a composition comprising an organic coating polymer of number average molecular weight of up to 3,000 which contains an acidic group (or a precursor thereof) and unsaturated groups optionally linked to the matrix polymer at least 25% w/w of which are vinyl groups.

This invention relates to filled cohesive polymer matrices and a processfor their production.

It is known to modify the properties of a variety of organic polymers byincorporating into such polymers or mixtures thereof one or moreinorganic fillers to enhance at least some of the physical properties ofthe polymer, for example the tensile modulus, tensile strength, orresistance to wear.

It is also known to enhance some of the interactive physical propertiesbetween a filler and the polymer matrix or precursor thereof in which itis used, and in turn to enhance the processability of thefiller-precursor mixture or the properties of the filled matrix, whichdepend on such interactive properties. Thus, to improve thedispersibility of the filler in the matrix, or to enhance tensilestrength and wear resistance of a filled polymer matrix inter alia, itis desirable to make such fillers and their matrix polymers as mutuallycompatible as possible and in the latter case to try to optimisefiller-polymer bonding. This may be achieved by coating the filler witha material having good filler-coating bonding and to surround it with amatrix having particularly good coating-matrix bonding.

However, in some polymer systems, such physical properties may beenhanced at the expense of the appearance of the filled polymer matrix,for example the occurrence of commercially unacceptable mottling.Surprisingly we have now found that this problem can be overcome byusing a specific class of filler coating polymers in such polymersystems.

Accordingly, in a first aspect the present invention provides a cohesivepolymer matrix comprising a matrix polymer and a coated particulatefiller dispersed therein, characterised in that the matrix polymer is asolution rubber, and the filler is coated at least in part with acomposition comprising an organic coating polymer of number averagemolecular weight of up to 3,000 which contains an acidic group (or aprecursor thereof) and unsaturated groups optionally linked to thematrix polymer at least 25% w/w of which are vinyl groups. Preferably atleast 30% w/w of such groups are vinyl groups.

The polymer matrix may comprise more than one solution rubber, at leastone other polymer or oligomer or an equivalent e.g. an extender, and/ormore than one particulate filler provided that at least one such filleris coated as described hereinbefore.

Preferably the or each filler is inorganic and finely particulate. Thecoating composition may contain more than one coating polymer ashereinbefore defined.

The term "solution rubber" herein includes synthetic rubbers which havebeen produced by solution polymerisation, such as (without limitation)EP, EPDM, butyl, SBR and nitrile rubbers, and polychloroprene,polyisoprene, and polybutadiene when so produced.

Such solution rubbers typically contain a plurality of unsaturated e.g.olefinic groups any of which may or may not be cross-linked. If notcross-linked, this unsaturation tends to make such a polymer curable toanother matrix of the present invention, for example a fluid or solidmatrix may be capable of cross-linking to form another, usually solid,matrix, and this can be used to further modify the properties of a widerrange of such rubbers. Precursor matrices which are convertible to othermatrices of the present invention are of specific interest, since it isoften such precursors which are used in the production process for thefilled matrices of the present invention (described further below).

Thus, the present invention in one embodiment of its first aspectprovides a precursor composition for the production of a filled cohesivesolution rubber matrix which composition comprises a dispersion of afiller and a dispersion and/or solution of a coating composition ashereinbefore defined in a matrix of a precursor of that solution rubber.

Within the scope of the term "precursor of an acidic group", areincluded all groups convertible to free acid groups (in particular underthe coating and matrix processing conditions described hereinafter), forexample salts, anhydrides and imides in particular such precursors ofcarboxylic acid and diacid functions.

The use of the particular present coating compositions and polymers inthe present solution rubber matrices confers particularly good physicalproperties on, or enhances particularly well the physical properties of,such coated fillers and filled matrices, whilst retaining good matrixappearance.

In the particular present matrices the matrix and their precursorspolymer(s) and coating polymers have good mutual compatibility andpreferably should be capable of mutual cross-linking or be mutuallycross-linked e.g. via unsaturated (especially olefinic eg vinylic)groups, to enhance coating-matrix and hence filler-matrix binding. Mostconventional solution rubbers or their precursors (of widely varyingchemical constitution) are believed and/or appear to have particularlygood compatibility with and/or ability to cross-link to the presentcoating polymers or compositions described further below.

If the matrix contains any matrix polymer or oligomer other than thesolution rubber(s), this material should of course be compatible withthe other components of the matrix, such as the solution rubber and thecoating polymer, and preferably be capable of cross-linking or becross-linked to such polymer components.

Similarly, the present coating polymers, and hence matrix polymers,appear to have not only the necessary compatibility with differentfiller materials, but to be versatile with a wide range of suchmaterials including inter alia amphoteric, basic, carbonaceous andsiliceous fillers.

Within the above general guidelines and those given hereinafter suitablematrix polymers and particulate fillers may be established by routinetrial.

Within solution rubbers as defined hereinbefore, the or each matrixpolymer may be a homopolymer or any type of copolymer (e.g. random,block or graft). It may be cross-linked or not.

Particularly useful solution rubbers include polydiene rubbers, such assythetic butadiene-based rubbers, e.g. butadiene-styrene (`SBR`) andbutadiene-acrylonitrile rubbers, (`nitrile`), ethylene-propylene (`EPM`)and ethylene-propylene-diene (`EPDM`) rubbers, e.g.ethylene-propylene-norbordiene rubbers, and polybutadiene, andpolyisoprene, which have been produced by solution polymerisation,optionally cross-linked internally and/or to the coating polymer. Theforegoing polymers may of course comprise (other) comonomers. Thesolution rubber may often be based on a monomer in common with thecoating polymer used with it, within the present matrices, e.g. a diene.Where this is the case, the coating polymer (described hereinafter)appears to bind well to conventional emulsion rubbers of this type.

In the precursor matrices of the present invention, preferred precursormatrix polymers are diene based rubbers which still containcross-linkable e.g. olefinic groups, preferably as part of the rubberstructure, to promote matrix and matrix coating bonding. Other matrixpolymers may suitably be inter alia homo- or co-polymers, -oligomers or-polycondensates based on vinylics, for example polyvinylchloride. Thelatter blended with a solution nitrile rubber is one suitable example ofsuch mixed matrix polymers. Equivalents of other matrix polymers includeextenders, e.g. oil extenders. EPDM with an oil extender is one suitableexample of such a matrix system.

The coating polymer within the filled matrix of the first aspect of thepresent invention is often one with a number average molecular weight inthe range 500 to 3,000 preferably in the range 750 to 1,500. Thesematerials tend to be liquids (albeit viscous) at room temperature.However, within the scope of the present invention the coating polymersmay vary widely in chemical and physical properties. Within the aboveranges the dispersibility of any coating polymer as a neat liquid, asolution or particles in the matrix or its precursor under theconditions of matrix formation (described hereinafter) or filler coating(conventional) should be sufficient for it to cover the filler surfaceadequately and evenly to the desired extent, and the molecular weightshould not be so high as to make the process matrix intractably viscous.This parameter will clearly tend to indicate to the skilled manpreferred coating polymers within the foregoing favoured materials. Formany types of these coating materials, preferred polymers will lie inthe molecular weight range of 750 to 1,400.

(All the foregoing molecular weights include the acid/precursor groupsand unsaturated groups within the coating polymer, and weightpercentages of such groups hereinafter are based on the weight of thetotal polymer including such groups).

The coating polymer contains a plurality of unsaturated groups. Theunsaturated groups are preferably olefinic. The coating polymer iscapable of reacting, or has reacted, with a cross-linkable matrixpolymer or its precursor, for example by free-radical or sulphidiccross-linking with a cross-linkable matrix polymer or its precursorwhich also contains olefinic unsaturation. The coating polymer ispreferably linked to the matrix polymer by such groups. At least 25%w/w, and preferably 30% w/w, of such olefinic groups will be vinylgroups in the particular present coating polymers.

Olefinic groups may be present as part of a structure which is theproduct of diene polymerisation; examples of such structures includepolymers and copolymers derived from one or more dienes, of which themost conveniently available is butadiene, although others may be used ifdesired (for example isoprene, chloroprene and 1,5-cyclooctadiene andmixtures thereof). Examples of other compounds which may becopolymerised with the diene or dienes include a wide range of vinylmonomers, for example, styrene, acrylonitrile, and mixtures thereof.

Conjugated diene polymerisation may proceed via 1,4-polymerisation toyield a linear skeleton with repeat units each with a corresponding2-ene group, and/or via 1,2-polymerisation to yield a skeleton withpendent vinyl groups corresponding to 3-ene groups. At least 25%, andpreferably 30%, w/w of any olefinic groups in such a product used in thepresent coating compositions will be such vinyl groups.

The probability and extent of coating-matrix bonding is of courseincreased in precursor matrices as hereinbefore described where thecoating and matrix polymers have olefinic unsaturation, and/or bymaximising the weight percentage of cross-linking eg olefinic groups ineach polymer (including polymer-chain and vinylic olefinic groups)commensurate with the relative proportion of matrix to coating polymer.

A preferred concentration of any unsaturated binding groups in thecoating polymer is at least one such group per 800 total polymermolecular weight, preferably at least 5% w/w of the polymer, inparticular at least 10% w/w.

Suitable acidic groups within the coating polymer include carboxylicacid and diacid groups. It is preferred that the polymer does notcontain acidic or basic substituents, since these tend to facilitateself-condensation of the coating polymer at the expense of the desiredbinding and linking. For this reason precursors of the acidic group(s)in which active hydrogen is reversibly removed are preferred over theacidic groups themselves, for example neutral salts or imides oranhydrides of the acidic group.

Suitable salt precursors include alkali metal (e.g. sodium), alkalineearth metal and in particular high alkyl quaternary ammonium salts ofcarboxylic acid groups.

Suitable anhydrides and imides include α, β-dicarboxylic cyclicanhydrides and imides, as terminal or non-terminal functions, such asthose derived from maleic anhydride or imide, not least because of thegenerally good compatibility of the relevant coating polymer withsolution rubbers and their precursors.

The desirability of good filler-coating and coating-matrix bonding ine.g. enhancing tensile strength and wear resistance of the polymermatrix has been referred to above. The present coating polymer appearsto bind well to conventional fillers. The general mechanism is notclear, but, without prejudice to the invention in general, in the caseof a basic filler the coating polymer is believed to chemically bond tothe surface of a basic filler within the matrix by reaction of theacidic group with the surface.

A preferred concentration of any acidic group or any precursor thereofin the coating polymer is at least one such group per 800 total polymermolecular weight, preferably at least 5 weight %, in particular at least10 weight % of the polymer.

The foregoing coating polymers belong to a known class of materials.

Most of the matrix polymers mentioned hereinbefore may also be used asan additional coating composition component.

It will be appreciated from the foregoing that precursor coatingpolymers which contain an unreacted unsaturated group (and which arethus still capable of cross-linking and/or linking to a matrix polymer)are of specific interest, since it is often such precursors which areused in the production process for the filled matrices of the presentinvention (described further below).

Such precursor coating compositions may contain additives appropriate tothe matrix formation reaction generally as up to 5 weight % each of thetotal composition e.g. an antioxidant, or a free radical initiator or avulcanising agent and/or sulphur to promote good intra-coating,coating-matrix and/or intra-matrix linking.

Often, however, the coating composition will consist essentially of thecoating polymer.

In the matrices of the present invention the proportions of matrixpolymer to filler to coating polymer may vary, and may be optimised togive desired physical properties by routine trail. Where the filler iscoated before incorporation into the matrix (see description of theprocess hereinafter) it is believed that the proportion of coating tofiller in the matrix is unchanged, (i.e. by virtue of the constitutionof the coated filler particles being unchanged). Where the coatingpolymer and uncoated filler are incorporated separately into the matrix(see process description hereinafter) it is unclear what the proportionsof coating polymer are eventually present as a filler coating and as`free` polymer in the product matrix, since the proportion of filler tofree coating polymer is modified during manufacture by binding of someof the free polymer to the filler surface. By no means all of the freepolymer necessarily disappears in this way; indeed, higher proportionsof coating polymer are generally used in these circumstances to ensureadequate filler coating.

For these reasons the matrix composition is best described in terms ofmatrix polymer or precursor:filler:coating polymer proportions and thesemay vary widely within the scope of the present invention, inter aliawith the density and specific surface area of the filler.

The proportion of the total matrix of matrix polymer may be as low as5%, that of the filler may be 0.15 to 95%, and of the coating polymer upto 50%, all percentages being by weight. Preferably the proprotion offiller is 0.15 to 55%.

Within the above ranges the dispersibility of the filler in the matrixpolymer and/or the coating polymer under the conditions of matrixformation (described hereinafter) should be sufficient for them to coverthe filler surface adequately and evenly. This parameter will clearlyindicate to the skilled man preferred proportions for given materials.

For a filler of relative density of about 2, and a specific surface areaof about 3 m² gm⁻¹ favoured proportions are 35 to 98% matrix polymer,1.5 to 75%, preferably 1.5 to 55%, filler and 0.5 to 15% coatingpolymer; favoured proportions for the other particle parameters willvary in a manner evident to the skilled person.

The matrix and any precursor thereof may also contain a conventionalanti-oxidant, suitably as up to 5 weight % of the matrix, and otherconventional additives, for example plasticisers, pigments, antiozonantsand extenders such as oil extenders.

Any particulate filler may be used in the present invention providedthat the filler is stable in the matrix polymer or a precursor thereof,and under any processing conditions, in particular under any fillerheating or coating, or matrix formation, conditions; it is howeverpreferred that the filler is capable of binding to or adsorbing thecoating polymer. The filler should of course desirably be insoluble inwater.

Suitable fillers include amphoteric, basic, carbonaceous and siliceousfillers.

The filler may e.g. be amphoteric, e.g. such an oxide, suitable suchfillers include oxides and hydroxides of aluminium, including hydratedalumina. Such fillers may be of natural or synthetic origin.

The filler, if basic, may be for example an oxide, a hydroxide, acarbonate or a basic carbonate. Suitable fillers include oxides,hydroxides, carbonate and basic carbonates of alkaline earth metals andof zinc. Preferred such fillers are the carbonates of calcium andmagnesium, basic magnesium carbonates, and magnesium hydroxide. Suchfiller particles may be of natural or synthetic origin. For example,calcium carbonate may be in the form of ground chalk or produced in theform of a precipitated calcium carbonate, for example calcium carbonateprepared by carbonation of milk of lime.

Suitable carbonaceous fillers include carbon blacks, for example furnaceblacks and thermal blacks, in particular medium thermal blacks.

Suitable siliceous materials may be natural or synthetic. Siliceousfiller particles may consist of substantially pure silica, for examplesands, quartzes or cristobalites or precipitated or fused silica, or maycontain silica together with a proportion of one or more other metaloxides, for example acidic oxides, e.g. titania, or metal oxides capableof forming silicates, e.g. calcium, magnesium, aluminium andcombinations of these. They may consist of a silicate, provided thesilicate is one which is suitable for use as a filler, for example if itis insoluble in water. Suitable silicates include clays and talcs whichcan be produced in a sufficiently finely divided form to serve asfillers.

The filler may comprise a silicate, for example it may be a silicatecoated alkaline earth metal carbonate as described in U.S. Pat. No.4,373,178.

It is less preferred that the siliceous particles consist predominantlyof silica and especially less preferred that they consist ofsubstantially pure silica itself.

Mixtures of all the foregoing particulate fillers may be used.

The filler particles for use in the invention may have any form suitablefor a filler, and may have a wide variety of particle shapes and sizes.For example, they may be of irregular, fibrillar or laminar form. Mostconveniently the particulate filler is a free-flowing finely-dividedpowder, as usually commerically available.

Most commonly the filler particles will have a size in the range 10Angstrom to 1 mm, though we prefer, on account of the good reinforcingeffect and high filler loading that is possible, that the particle sizeis in the range 0.01 to 100 micron, e.g. 0.05 to 20 micron. Typicallythe particles will have a specific surface area of 0.1 to 250 m² g⁻¹,preferably 1.5 to 75 m² g⁻¹, in particular 2 to 25 m² g⁻¹.

For high filler loadings the particles may be a mixture of two sets ofparticles with two widely differing mean sizes such that one set ofparticles can fit in the interstices of the other within the matrix.

In a second aspect the present invention provides a process for theproduction of a filled cohesive solution rubber matrix, which processcomprises intimately mixing a matrix solution rubber or a precursorthereof with

(a) a filler and a coating composition or precursor thereof ashereinbefore defined, or

(b) a filler coated with a coating composition or precursor thereof, andthereafter as necessary converting any solution rubber precursor in themixture to a solution rubber matrix.

Variant (a) is preferred.

A mixture of matrix polymers and/or precursors may of course be used.Precursors of the matrix polymers and/or compositions are preferred.

Where any linking reactions are in the second process (conversion) stepand involve any matrix polymer, they are part of a conventional matrixcuring process. This may be effected conventionally, e.g. by heating toset a thermosetting polymer or its precursor, or by heating, processingand cooling for a thermoplastic. Radiation curing may also be used.

The mixing step in either process variant may be carried out byconventionally blending the matrix polymer or precursor with the coatedfiller or with the coating polymer or precursor and the filler, forexample by milling e.g. using a ball-mill or multi-roll mill orhigh-shear mixing or mixing in a planetary vacuum mixer.

It may be helpful to apply some heat, in either process step. Suitablereaction temperatures may vary over a wide range below that which isdeleterious to any component, but will typically be in the range of 15°to 200° C., for example ambient. The application of heat may bedesirable both for ease of application of fluid coating and/or matrixprecursor compositions (the viscosity of which generally decreasesusefully with rising temperatures) and, as may be desired, to promoteany linking reactions.

Process times are typically in the range 1 minute to 6 hours. Ambientpressure is suitable.

The coating polymer or its precursor is often conveniently liquid (evenif a viscous liquid) at ambient temperatures or in the form of a freeflowing powder with a melting point range within the range of 20 to 230,more conveniently 20° to 130° C. The convenience of such properties inthe present processes will be readily appreciated.

The process may be carried out in the presence of protecting agents,e.g. antioxidants, and/or in an inert atmosphere, e.g. nitrogen, argonor solvent vapour, if it is desired to guard against deterioration ofthe polymer during any heating that may be necessary, and withconventional additives (e.g. processing aids), such as mentionedhereinbefore as optional components of the coating composition precursoror the matrix precursor, e.g. for linking reactions, which may beincorporated in either or both, before or during the preparativeprocess.

In preferred process variant (a), not all of the coating polymer of thepresent invention may coat the filler, but coating in this processvariant appears not to be hampered. However, it may be desirable to usean excess of coating polymer/composition over that theoretically neededto coat the filler alone to the desired extent.

The coated fillers for use in variant (b) belong to a known class ofsuch fillers and may be prepared by known methods. Preferably they arecoated with a proportion of coating polymer/composition or precursorthereof which produces a matrix composition within the ranges mentionedhereinbefore.

Each filler particle will often be on average at least 95% coated,favourably fully coated. However, partially coated particles may beacceptable, for example at least 40%, favourably at least 75%, coated.

In both process variants of course the process components are generallya continuous or particulate fluid, and there must also be sufficient ofone or more matrix polymers or precursors to flow and mix with, andfully enclose the filler particles and ensure good dispersion of thefiller through the product matrix. Suitable proportions within theranges given hereinbefore can be determined by simple trial and are notnecessarily critical. In either process variant, there may also be useda vehicle (solvent or dispersant) for the matrix polymer and/or thecoating composition to assist the spread of the matrix polymer and/orcoating over the filler (especially when the coating represents a lowproportion of the matrix and/or the coated filler).

Any such vehicle may be chemically inert and should be of lowflammability and low toxicity, and, where the desired product matrix isa solid, a low boiling point will tend to be significant in thesubsequent necessary removal of the vehicle from the mixture.

It may in some cases be convenient to use a vehicle which containsunsaturation, e.g. olefinic or acrylic unsaturation, in particular wherea precursor coating or matrix polymer contains unreacted unsaturation ofthe same type. Such a vehicle will of course in general be capable oftaking part in any concomitant or subsequent linking reactions, e.g.with a coating and/or matrix polymer precursor, advantageously topromote matrix-filler linking.

The desired polymer matrix may be a fluid, such as a sealant orhigh-build surface coating, in which the matrix polymer is a solution,or emulsion or other dispersion in a vehicle. In such a case theprocessing vehicle may be retained as the vehicle for the final product.

Suitable conventional vehicles and their proportions in the process (andoptionally in the desired product) will be well-known to the skilledman, or can be readily determined by simple trail.

Matrix cross-linking, matrix-coating linking, coating cross-linking, andor coating-filler linking reactions may be incorporated in either orboth steps. Cross-linking or linking reactions may involve the matrixpolymer(s) or precursor(s), the coating polymer of the invention, andany other polymer in the coating.

Linking of the types above may take place separately or concurrentlywhen any of the foregoing polymers/precursors are of the followingpreferred types:

Preferably the coating composition comprises a coating polymer in whichall the unsaturation is olefinic, in particular a polydiene basedpolymer. Preferably also the or at least one solution rubber precursoris a compound which may be linked internally or with the coatingpolymer, in particular with a polydiene based coating polymer, butotherwise may be of widely varying chemical constitution. Examples ofsuch precursors for use in the process of the present invention includethe non-cross-linked polymers corresponding to any cross-linked polymersin the product matrix.

The filler and the coating polymer are preferably capable of good mutualbonding. A basic filler and coating polymer which comprises at least oneterminal or non-terminal cyclic anhydride or imide group (in particulara carboxylic such group) as an acidic group precursor are amongstpreferred filler coating combinations.

Where a basic filler is coated by a coating composition comprising apolymer containing an acidic group precursor group, it is desirable toconvert that precursor group to the acidic group, so that the filler iscoated at least in part with coating polymer which is bound to thefiller surface. This is conveniently effected in situ in the matrixformation/coating process by incorporating a converting reagent in theprocess. Thus, for example, where the precursor is an anhydride, asuitable reagent is water, either as reactable water within the filleritself or within any vehicle used.

We have found that the coating composition or precursor used in thepresent invention acts as a good dispersant for filler particles inmatrices of solution rubbers or their precursors, and accordingly in athird aspect the invention provides the use of such coating compositionsas dispersants for fillers in such matrices.

The preparation of filled polymer matrices of the present invention isillustrated by the following Examples. The preparation of coatingpolymer materials is illustrated by the following Description, whereinall parts and percentages are by weight.

DESCRIPTION Preparation of Organic Coating Polymer MPBD's (MaleinisedPolybutadienes)

Maleinised polybutadiene was prepared by the reaction of polybutadiene(100 parts) with maleic anhydride at 180°-190° C. for six hours under anitrogen atmosphere., with an antioxidant.

Each polybutadiene consists of 40-50% vinyl- 1,2; 30-40% trans- 1,4; and15-25% cis- 1,4 unsaturation.

The following were so prepared

MPBD(1)=butadiene M_(n) =1300, anhydride 10%

MPBD(2)=butadiene M_(n) =1300, anhydride 20%

MPBD(3)=butadiene M_(n) =1300, anhydride 40%

MPBD(4)=butadiene M_(n) =900, anhydride 20%

Some of the above products were subsequently conventionally hydrolysedto give the corresponding free acid form of the MPBD. The composition ofthese, based on anhydride was:

MPBD(5)=butadiene M_(n) =900, anhydride 20%

MPBD(6)=butadiene M_(n) =1300, anhydride 20%

EXAMPLE

Polymer matrices of the following compositions were compounded on a twinroll mill as in process variant (a) described hereinbefore. (i.e. withdirect compounding of inter alia matrix emulsion rubber, uncoated fillerand a dispersion of a coating composition in the mixture). The matriceswere then press cured at 160° C. (sulphur cures) or 180° C. (peroxidecures), cure times being determined by a Monsanto rheometer.

COMPOSITION 1

    ______________________________________                                                                Parts by                                                                      weight                                                ______________________________________                                        Matrix Polymer: EPDM, Vistalon 3666 (Esso)                                                              200                                                 (including an oil extender)                                                   Filler: Talc (Mistron Vapour RP6D)                                                                      171                                                 Coating Composition: MPBD (2)                                                                           5.1                                                 Other:                                                                        ZnO                       5.7                                                 Stearic Acid              2.3                                                 Vulcafor TMTM (Vulnax Internat Ltd)                                                                     1.8                                                 Vulcafor MBT (Vulnax Internat Ltd)                                                                      1.8                                                 Vulcafor TMTD (Vulnax Internat Ltd)                                                                     0.9                                                 Sulphur                   1.8                                                 Cure time: 16.2 min                                                           ______________________________________                                    

COMPOSITION 2

As for composition 1, but using clay (Supreme, English China Clays) inplace of talc. Cure time 16.9 min.

COMPOSITION 3

As for composition 1, but using: Precipated CaCO₃, Calofort U (J ESturge) in place of talc, and MPBD(1) 3.4 parts in place of MPBD(2) 5.1parts. Cure time: 11.8 min.

COMPOSITIONS 4, 5 and 6

As for composition 3, but using respectively MPBD(2), MPBD(3) andMPBD(4) in place of MPBD(1). Cure times respectively 12.6, 13.5 and 12.0min.

COMPOSITION 7

    ______________________________________                                                              Parts by                                                                      weight                                                  ______________________________________                                        Matrix Polymer: EPDM, Vistalon 3666                                                                   175                                                   Filler: Precipitated CaCO.sub.3, Calofort U                                                           150                                                   Coating Composition: MPBD(5)                                                                          3                                                     Other:                                                                        ZnO                     5                                                     Stearic Acid            2                                                     Vulcafor TMTM           1.6                                                   Vulcafor MBT            1.6                                                   Vulcafor TMTD           1.6                                                   Sulphur                 1.6                                                   Cure time: 10.7 min                                                           ______________________________________                                    

COMPOSITION 8

As for composition 7, but using MPBD(6) in place of MPBD(5). Cure time12.3 min.

COMPOSITION 9

    ______________________________________                                                              Parts by                                                                      weight                                                  ______________________________________                                        Matrix Polymer: EPDM, Vistalon 3666                                                                   350                                                   Filler: Precipitated CaCO.sub.3, Calofort U                                                           300                                                   Coating Composition: MPBD(1)                                                                          6                                                     Other                                                                         ZnO                     10                                                    ATM3 (Ancomer Ltd)      4                                                     Permanax WSP (Vulnax)   2                                                     Perkadox 14-40B (AK20)  12                                                    (Peroxide cure). Cure time 11.0 min                                           ______________________________________                                    

COMPOSITIONS 10, 11 and 12

As for composition 9, but using respectively MPBD(2), MPBD(3) andMPBD(4). Cure times respectively 11.4, 12.5 and 12.6 min.

Medium thermal carbon black may be used in any of the foregoingcompositions in place of the filler therein.

EXAMPLE 2

All the final, filled and vulcanised matrices were found to have goodappearance and were tested in accordance with the following procedures.

Tensile stress-strain properties were measured in an Instron 1122Tensile Testing Machine according to BS903 part A2 using dumbels cutfrom 2 mm thick sheet. Tear strength properties were measured accordingto DS 903 part A3 using method c-crescent shaped test pieces cut from 2mm thick sheet and nicked using a Wallace Tear Test Specimen NickingCutter.

Hardness was measured on 4 mm thick sheet accordingly to BS 903 part A26 using a Wallace Dead Load Hardness Tester for Rubber.

Rebound resilience was measured on 4 mm thick sheet according to BS 903part A8 using a Dunlop Tripsometer with a drop angle 45°.

Compression set was measured according to BS 903 part A6 using a Wallacecompression set apparatus. The results were calculated from plugssubjected to a 25% compressive strain for 24 hours at 70° C.

Volume swell was measured on 2 mm thick sheet according to BS 903 partA16 using a volumetric method. The results were calculated on samplessubjected to distilled water at 95° C. for 72 hours.

These properties are shown in the following Table.

                                      TABLE                                       __________________________________________________________________________    FILLER PERFORMANCE IN MATRICES OF EXAMPLE 1                                         300%   TENSILE                             VOLUME                       COMPO-                                                                              MODULUS                                                                              MODULUS                                                                              % ELONGATION                                                                            TEAR STRENGTH                                                                            REBOUND SWELL HARDNESS               SITION                                                                              MPa    MPa    TO BREAK  Nmm.sup.-1 CRESCENT                                                                      RESILIENCE                                                                            %     (IRHD)                 __________________________________________________________________________    1     4.0    7.4    727       28.6       56            54                     2     5.5    10.3   718       37.7       51      1.3   55                     3     3.5    11.0   692       27.7       54      -0.1  55                     4     3.7    11.2   670       25.3       56      -0.2  57                     5     3.4    10.9   655       21.7       59      -0.3  57                     6     3.7    12.4   691       35.8       57      -0.3  55                     7     3.7    10.9   636       26.2       60      -0.2  58                     8     4.0    12.3   687       47.0       58      -0.6  59                     9     3.8    10.0   638       29.2       54      0.3   52                     10    4.4    10.2   601       28.4       54      0.2   52                     11    4.5    9.7    593       30.7       55      0.5   52                     12    4.3    10.2   624       28.6       55      0.0   51                     __________________________________________________________________________

We claim:
 1. A cohesive polymer matrix comprising:a matrix polymer and acoated particulate filler dispersed therein, characterized in that thematrix polymer is a solution rubber, and the filler is coated, at leastin part, with a composition comprising: an organic coating polymer ofnumber average molecular weight in the range 750 to 1,400 which containsan acidic group (or its salt, imide, or anhydride) and unsaturatedgroups either bonded or non-bonded to the matrix polymer at least 30%w/w of which are vinyl groups.
 2. A matrix according to claim 1,characterised in that the matrix polymer is a solution EPDM rubber.
 3. Amatrix according to claim 1, characterized in that it, as a precursormatrix, can cross-link to another said matrix and comprises a dispersionof a filler and a dispersion or solution of a coating composition, asdefined in claim 1, in a matrix of a non-cross-linked solution rubber.4. A matrix according to claim 3, characterized in that it cancross-link to form another said matrix by reaction of a crosslinkingfunctional group in the coating polymer or the matrix polymer with afunctional group on the matrix polymer or an additional matrix polymer.5. A matrix polymer according to claim 4, characterised in that thecross-linking function is an olefinic group.
 6. A matrix according toclaim 1, characterised in that the coating polymer comprises at least 5weight % of unsaturated groups.
 7. A matrix according to claim 1,characterised in that the coating polymer is a substituted polybutadieneor polyisoprene.
 8. A matrix according to claim 1, characterised in thatthe coating polymer comprises an α,β-dicarboxylic cyclic anhydride groupor the product of the reaction of the same with the filler surface.
 9. Aprocess for the production of a filled cohesive solution rubber matrixaccording to claim 1, said process comprises intimately mixing a matrixsolution rubber with:a filler and a coating composition as defined inclaim 1 or a filler coated with a coating composition and thereafter asnecessary chemically converting unreacted solution rubber to form thesolution rubber matrix.